GB2232684A

GB2232684A - Making roller-bearing elements

Info

Publication number: GB2232684A
Application number: GB9007163A
Authority: GB
Inventors: R Frank Hengerer
Original assignee: SKF GmbH
Current assignee: SKF GmbH
Priority date: 1989-04-05
Filing date: 1990-03-30
Publication date: 1990-12-19
Anticipated expiration: 2010-03-30
Also published as: FR2645544A1; GB2232684B; DE3910959A1; FR2645544B1; DE3910959C2; JPH02285024A; GB9007163D0

Description

1 Process for the Production of Rolling-Bearing Elements From Through-

Hardening Rolling-Bearing Steel

The present invention relates to a process for producing rolling-bearing elements from through-hardened rolling-bearing steel in accordance with the preamble to Claim 1.

In a known process of this kind, after being cooled from the forging heat, the blank is soft-annealed at 650 to 815 0 C and then machined by cutting (DE-AS 2.023-101). The process step of annealing is expensive in time and energy, however. To this must be added the fact that during this annealing, a large cementite grain forms in the structure so that after the austenitizing, quenching and tempering there are still coarse carbide precipitations in the hardness structure. In order to achieve an optimum strength of the rolling-bearing element with a correspondingly long life, however, the carbide precipitations of the hardness structure in the rolling-bearing element should be as fine-grained as possible.

It is the object of the present invention to provide a process of the kind indicated which can be carried out with little expenditure of time and energy and at the same time yields a hardness structure which imparts an exceptionally long life to the rolling-bearing element.

According to the present invention there is provided a process for the production of rolling-bearing elements from through-hardened rollingbearing steel, wherein a blank - is heated to a first austenitizing temperature of about 11500C and is austenized and shaped at this temperature, - is then cooled in gas to ambient temperature so that a lamellar pearlite structure results, - is rough-machined, - is heated to a second austenitizing temperature below the first austenitizing temperature and is kept at this temperature to form a homogeneous austenite with carbides distributed in a finely dispersed manner, - is quenched in oil, salt or water so that a hardness of at least 64 HRC results, and - is finish-machined into a rolling-bearing element, characterised in that, after being cooled in gas, the blank is rough-machined in the lamellar pearlitic state and immediately afterwards is heated to the second austenitizing temperature.

No soft-annealing is necessary any more during the production of the rolling-bearing element in accordance with the invention. The heat treatment of the blank can therefore be carried out economically in a short time with little expenditure on heating energy.

After the blank has been cooled in gas, for example air or nitrogen, the relatively hard lamellar pearlitic blank can be roughly machined on a lathe with particularly long-lasting turning tool edges of ceramic material or hard metal.

The process according to the invention has the great advantage that it provides a homogeneous hardness structure with very fine carbide precipitations in the rolling-bearing element. The rolling-bearing element produced by this process has a surprisingly long wear and fatigue life in its rolling track and this is so even when the latter is lubricated with a lubricant which picks up small abraded particles or particles of dirt in operation.

Advantageous measures of the process according to the invention are characterised in the sub-claims.

Claims

With the measure according to Claim 2, the effect is achieved that the scale forming during the hot rolling, forging and/or hot pressing is removed from the surfaces of the blank. The measure according to Claim 3 has the effect that as a result of the cooling of the blank in gas, a particularly homogeneous lamellar pearlite forms in the blank. If the measure according to Claim 4 is used, the rough machining i-, carr4-d out with the extremely long-lasting tool edges which may consist of hard ceramic oxides, carbides and/or nitrides. Claims 5 to 8 indicate further advantageous measures. Preferably, a process according to the invention for the production of rolling-bearing elements from through-hardening rolling bearing steel is effected with a blank, - which is heated to a first austenitizing tcmperature.of 11500C so that it is austenized, whereby all the carbides are dissolved in the structure and is also shaped at this temperature, for example by forging (see drawing "hot shaping"), - which is then cooled in gas, for example in moving air or;In moving nitrogen, to ambient temperature so that a fine lamellar pearlite structure results: This cooling is best effected in the range from 900 to 650 0 C at a speed of about 400C/minute, - which is roughly machined in this pearlitic structure state, for example with a ceramic-coated turning tool, (see drawing "roughmachining"), - which is then heated to a second austenitizing temperature which is lower than the first austenitizing temperature and may be about 840 OC, and is held at this temperature sufficiently long, for example 20 minutes, until the formation of a homogeneous austenite with uniformly distributed secondary carbides (see drawing "hardening"), which is then quenched in oil, salt or water to achieve a hardness of at least 64 HRC, and - which is finally finish-machined by grinding and/or honing to form a rolling-bea-_-'n1,Y e-'-.r,snt. A tempering of the blank may also be interposed after the quenching and before the finish-machining of the blank. This tempering is best effected in the range of 160 to 240 0 C with a holding time from 1 to 2 hours so that a hardness in the range from 58 to 64 HRC is achieved (see drawing "tempering"). In addition, blasting with sand or the like may also,be effectcd between the cooling of the blank in gas and its rough-machining by cutting, so that any scale which may have formed is removed from the surfaces of the blank before it is machined. A rolling-bearing steel which has the following percentage composition is suitable for use in the process: C 0.90 - 1.10 Si Mn 0.15 - 0.35 0.25 - o.4o 1 Cr S p 1. 30 1. 65 at most 0.025 at most 0.030 the rest being iron and impurities due to smelting. Ihe rolling-bearing element produced from this sort of steel by the process according to the invention has a particularly long fatigue life in its rolling track. This long fatigue life still occurs even if small particles of foreign bodies, for example abraded particles, should be present in the lubricating oil. CLAIMS:

1. A process for the production of rolling-bearing elements from throughhardened rolling-bearing steel, wherein a blank - is heated to a first austenitizing temperature of about 11500C and is shaped at this temperature, - is then cooled in gas to ambient temperature so that a lamellar pearlite structure results, - is rough-machined, - is heated to a second austenitizing temperature below the first austenitizing temperature and is kept at this temperature to form a homogeneous austenite with carbides distri.bu4-,-.d 4-- a finely dispersed manner, - is quenched in oil, salt or water so that a hardness of at least 64 HRC results, and - is finish-machined into a rolling-bearing element, characterised in that, after being cooled in gas, the blank is rough-machined in:Ae lamellar pearlitic state and immediately afterwards is heated to the second austenitizing temperature.

2. A process according to Claim 1, characterised in that, after being cooled in gas, the blank is blasted with sand or the like.

3. A process according to Claim 1 or 2, characterised in that the cooling of the blank in gas is effected in the range 900 to 6500C at a speed of about 40 0 C/min.

1

4. A process according to any one of the preceding claims, characterised in that the machining of the blank by cutting is carried out with a tool having a cutting edge of a ceramic material.

5. A process according to at least one of the preceding claims, characterised in that the heating to the second austenitizing temperature at a temperature of about 840 0 C is effected with a holding time of about 20 minutes.

6. A process according to any one of the preceding claims, characterised in that, after being quenched at 160 to 240 0 C, the blank is tempered with a holding time of 1 to 2 hours.

7. A process according to any one of the preceding claims, characterised in that the finish-machining of the blank is effected -grinding and/or honing.

8. A process according to any one cf rhe preceding claims, characterised by the use of a steel having the composition, in percentages, of 1 C si Mn Cr S p 0.90 - 1.10 0.15 - 0.35 0.25 - o.4o 1.30 - 1.65 at most 0.025 at most 0.030 the rest being iron and impurities due to smelting.

9. A process for the production of rolling-bearing elements from throughhardened rolling-bearing steel, the process being substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.

J Published 1990 at ThePatentOffice. State House.66 71 High Holborn. London WClR4TP. Further copies 3naybe obtained from The Patent Office Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87